Arsenic concentration and mass flow rate in natural waters of the Valles caldera and Jemez Mountains region, New Mexico

This paper details the spatial and temporal occurrence of arsenic concentrations and mass flow rates along the Jemez River and the Rio Grande in north-central New Mexico. Samples of river water, hot springs, and cold springs were collected at 25 locations during November 1994, March 1996, and June 1996. Arsenic and other trace metal analyses were performed by graphite furnace and hydride generator atomic absorption spectroscopy for acidified unfiltered samples. Concentrations along the Jemez River ranged from 2 to 300 micrograms per liter (µg/L). Seven of ten locations exceeded the current EPA arsenic drinking water standard of 10 µg/L. These seven locations were at or downstream of the Jemez Springs area where roughly 1,500 L/min of thermal water enters the river from the Valles caldera geothermal system. In the Jemez Springs area, the thermal water can be sampled directly from Soda Dam hot spring and Travertine Mound hot spring. Discharge from these hot springs flows directly into the Jemez River. From Soda Dam hot spring, the arsenic concentration was 1,770 µg/L and the mass flow rate was 0.02 kg/day. The Travertine Mound hot spring arsenic concentration was 830 µg/L, and the mass flow rate was 0.001 kg/day. The highest arsenic mass flow rate on the Jemez River was approximately 6 kg/day at a location below Soda Dam hot spring and decreased to 0.1 kg/day below the Jemez Canyon Dam. All six sampling locations along the Rio Grande between